In rotatable cutting tools having a cutting head that is separable from a driving element such as a shank, it is necessary that the driving interconnection between the two be as rigid as possible while allowing them to be relatively readily assembled and disassembled.
German published patent application DE 31 30 484 A1 discloses a rapid change tool holder comprising a shank and a head. The head carries a cutting insert and is detachably clamped to the shank. The facing end surfaces of the shank and the head are shaped to provide a "multiple form-locking" of one to the other. The multiple form-locking that is disclosed comprises two protrusions on the shank, each having the cross section of an equilateral triangle, and two facing recesses in the head for receiving the protrusions, wherein the dimensions and pattern of the recessed end is the exact negative of the protrusions on the shank. This multiple form-locking is described as providing high stability, however the rigidity of this interconnection is limited due to one part being an exact negative of the other.
The means for clamping the head to the shank in DE 31 30 484 A1 includes a tensioning bolt which passes axially through the shank and which has a formed end that is approximately T-shaped in cross section. This formed end is receivable in a correspondingly shaped mounting recess in the head. However the mounting recess includes an end stop and the arrangement is such that the head can be assembled on the shank from one sideways direction only. Furthermore the head must be accurately positioned for the formed end to enter the mounting recess. This restricts the ease and therefore the rapidity with which one head can be exchanged for another on the shank.
DE 31 30 484 A1 also discloses that the end stop of the mounting recess in the head may include a screw. This would allow sideways adjustment of the position of the head relative to the shank, but the amount of such adjustment is quite limited.